Photosensitive glass structures have been suggested for a number of micromachining and microfabrication processes such as hollow microneedle arrays being developed for transdermal drug delivery and the withdrawal of body fluids for biomedical and other applications. Unfortunately, silicon microfabrication processes are long, difficult, and expensive. These microfabrication processes rely on expensive capital equipment; X-ray lithography and deep reactive ion etching machines which generally cost in excess of one million dollars each and require an ultra-clean, high-production silicon fabrication facility costing millions more.
Anisotropic-etch ratios for FOTURAN® have generally been reported to be about 20:1 when exposed using high-powered (non-laser based) broad spectrum mid-ultraviolet flood lamp, but one paper notes an increased aspect ratio obtained when the photostructurable glass is patterned with a laser: “Effect of Laser Parameters on the Exposure and Selective Etch Rate in Photostructurable Glass” by Frank E. Livingston, et al., published in the Proceedings of the SPIE Vol 4637, pp. 404-12 notes at the top of page 410 that “In this high power regime, the measured etch rate ratio remained constant at ˜30:1.” (See also FIG. 7 on the same page 410, labeled “Etch rate ratio versus incident laser power for FOTURAN®”). The prior art glass microfabrication processes have had etch ratios of 30:1 when patterned with a laser and 20:1 when patterned with a flood lamp, resulting in a microstructure with a large wall slopes. Photostructured microneedles and other micromachined structures such as micro-lenses suffer precision due to excessive wall slope.